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Great Lakes Monthly Water Level Forecasts

From US Army Corps of Engineers

Great Lakes Weekly Water Level Forecasts

From US Army Corps of Engineers

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Lake Regulation News Releases

From the International Joint Commission

Lake Superior

The Board expects the total St. Marys River flow in June to be 2,070 m3/s (73,100 cfs), as prescribed by Regulation Plan 2012. Actual hour-to-hour and day-to-day flows may vary depending on hydrologic conditions, as well as variations in flow from the hydropower plants.

Anglers and other users of the St. Marys Rapids need to be cautious of the changing flows and water levels that will be experienced in the rapids in June. Gate #16 will be opened to a setting of 5 cm on Thursday, June 6 to facilitate sea lamprey trapping. Otherwise, the gate setting of the Compensating Works will be maintained at the current setting (Gates #7 – #14, 100 cm open, equivalent to approximately four gates fully open) through mid-June. To facilitate underwater inspections of the International Bridge piers, gates will be temporarily lowered to a setting equivalent to one-half gate open later this month. A supplementary news release will be issued once inspection dates and gate settings are finalized. Following these inspections, it is expected that the gates will be returned to a setting equivalent to approximately four gates fully open. The average St. Marys Rapids flow in June is expected to be approximately 428 m3/s, to meet the Plan 2012-prescribed flow in June in consideration of the capacity restrictions at the hydropower plants. Gate #1 will remain at its typical setting which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike. 

Water level changes over the month of May
Water supply conditions were drier than average in the Lake Superior basin and wetter than average in the Lake Michigan-Huron basin in May.
 Lake Superior rose by 7 cm (2.8 in) last month while the seasonal long-term average pattern is for Lake Superior to rise by 10 cm (3.9 in) in May.
 Lake Michigan-Huron rose by 10 cm (3.9 in) last month, and the seasonal long-term average pattern is for Lake Michigan-Huron to rise by 8 cm (3.1 in) in May. 

Water levels as of the beginning of June
 At the beginning of June, the lake-wide average water level of Lake Superior was 5 cm (2.0 in) below the seasonal long-term average (1918-2023) and 31 cm (12.2 in) below the level of a year ago.
 At the beginning of June, the lake-wide average water level of Lake Michigan-Huron was 8 cm (3.1 in) above the seasonal long-term average (1918-2023) and 7 cm (2.8 in) below the level of a year ago. 

 

Lake Ontario

The International Lake Ontario-St. Lawrence River Board is providing this notice to summarize winter conditions and water levels as spring is emerging.  Plan 2014 is a set of rules that govern Lake Ontario outflows through the Moses-Saunders Dam located between Massena, New York and Cornwall, Ontario.  The purpose of the plan is not to keep water levels at their average (which is impossible), but rather the levels will fluctuate with varying weather-driven water supply conditions, while trying to moderate extreme high and low water levels.

The seasonal rise of Lake Ontario will depend on future conditions, which are impossible to accurately predict. The Board will continue to monitor conditions and ensure outflows regulated by Plan 2014 are consistent with Orders of Approval

Snowpack

  • There was below average snowpack in the Lake Ontario – St. Lawrence River basin and the Ottawa River basin in winter 2023/2024. 
  • It is important to note that the correlation between the snowpack in the Lake Ontario basin and its subsequent spring and summer water levels is very low. 
  • The reason the correlation is weak is that there are many other factors that affect the spring runoff and which are difficult to estimate or predict, including how frozen the ground is when the snow melts, the moisture content of the soil, how fast the snow melts, and most crucial is how much it rains as the snow is melting and afterwards, which can increase runoff dramatically. 
  • While snowpack was below average this winter, recent rainfall has increased runoff and raised water levels.  The amount of rain received in the coming weeks will have the largest impact on peak water levels this spring.

Water Levels

  • Lake Ontario water levels have been near seasonal long-term average values (within +/-10 cm or 4 inches) so far in 2024.
  • Lake St. Lawrence levels are slightly below average, similar to those observed last year. Northeast winds the first week in April caused a temporary decrease in water levels. 
  • Water levels in the lower St. Lawrence River (Lake St. Louis and Montreal) are also near average and have risen in recent weeks in response to recent rainfall and Ottawa River flows (Ottawa River Regulation Planning Board – Ottawa River Regulation Planning Board )

Spring Outlook

  • Long term weather forecasts are typically informative up to about 10-days and according to the National Oceanic and Atmospheric Administration, a 10-day forecast has an accuracy of about 50 percent. 
  • A short-term forecast of five days is accurate approximately 90 percent of the time.
  • Due to weather forecast variability, a forecast of Lake Ontario lake-wide average water levels is produced weekly and shows potential, future, water levels based on recent and expected short-term weather conditions and long-term seasonal patterns.
    • The forecast represents the projected range of water levels that may be expected to occur under potentially wet, average, and dry conditions. 
    • The red area in the forecast conditions is known as the cone of uncertainty and the further into the future from the current date, the less certainty exists. 
    • Actual water levels will depend primarily on weather and water supplies, and during periods of extreme conditions, may fall outside of the projected range, above or below the red area. 
    • This forecast employs an ensemble forecasting methodology, whereby a set of over 100 water supply scenarios based on historical records are run through a binationally coordinated regulation and routing model to produce a corresponding set of simulated water levels and flows.   
  • Recent forecasts indicate a greater chance of water levels remaining below long-term average vs. being above long-term average through the next six months.  The forecast shows a small probability, should there be very dry conditions, of water levels dropping below the low H-14 criterion in mid-August. If water levels decrease below the low H14 thresholds, the Board would have authority to consider deviating from Plan 2014. 
  • Water levels in the Great Lakes and St. Lawrence River vary from year-to-year and throughout the year depending on weather-driven water supply conditions. Everyone should be prepared to live within the full range of levels that have occurred in the past and of those that may occur in the future.
  • Similar mid-April levels have been experienced on Lake Ontario in recent years since 2000, summarized in the table below. In 2001, the Lake Ontario level continued to rise in small increments and peaked at 75.01 m in mid-July. In 2006, the Lake Ontario level peaked in late-July at 75.03 m. Peak levels in 2001 and 2006 are similar to peak level that may occur with average water supply conditions this year.
    • The seasonal rise of Lake Ontario will depend on future conditions, which are impossible to accurately predict. The Board will continue to monitor conditions and ensure outflows regulated by Plan 2014 are consistent with Orders of Approval from the International Joint Commission, as directed by the governments that approved the plan.

 

Surface Water Temperatures – Departures from Average

from the National Oceanic and Atmospheric Administration (NOAA)

Average Surface Water Temperature from the Great Lakes Surface Environmental Analysis (GLSEA)

Ice Conditions

from the National Oceanic and Atmospheric Administration (NOAA)

Current Ice Cover Conditions

Snowpack Conditions

from the National Oceanic and Atmospheric Administration (NOAA)

Interactive Snow Information

90-Day Weather Outlooks

from the National Oceanic and Atmospheric Administration (NOAA)

Three-Month Outlooks – Official Forecasts

Temperature

Precipitation